1. Field of the Invention
The invention relates to a gear ring pump, particularly for use in small pump assemblies, which are preferably driven by an electric motor, produced as modular pumps, and used in vehicle and engine construction.
2. Description of the Related Art
Gear ring pumps, for example in the design of gerotor pumps, are used in vehicle and engine construction, in internal combustion engines, among other things, as fuel pumps or as oil pumps.
The rotor set used in gerotor pumps consists of an inner rotor having gear teeth on the outside and an outer rotor having gear teeth on the inside, whereby the inner rotor is connected with the drive shaft in torque-proof manner and has fewer teeth than the outer rotor, and the outer rotor is mounted so as to rotate in a cylindrical chamber of the pump housing, in such a manner that the teeth of the inner rotor, which is mounted eccentric to the outer rotor, mesh with the teeth of the outer rotor in certain regions.
In the pressure and suction region of the rotor set, kidney-shaped pump chambers (pressure and suction kidney(s)) are disposed in the pump housing, which stand directly in connection with pressure and suction connector lines disposed on the pump housing, and guarantee that the fluid to be pumped is pressed from the suction connector line into the pressure connector line, by way of the rotor set.
A hydrostatic drive unit of a lawn tractor, based on a gerotor pump and a gerotor motor is described in U.S. Pat. No. 7,614,227 B2, in which the oil volume stream from the pump to the hydromotor is regulated by means of a rotating control valve in the embodiment of a rotating plate. In this design, disclosed in U.S. Pat. No. 7,614,227 B2, a stationary bearing plate is disposed between the rotating plate and the gerotor motor, in which plate a bearing bore, for rotatable mounting of the motor shaft, is disposed in the center. Furthermore, two kidney-shaped passage openings are disposed in this bearing plate, in the region of the pump chambers of the gerotor motor, so that the bearing plate simultaneously takes on the task of a guide body and so that regulation of the travel drive of the lawn tractor, i.e. regulation of its speed and of its travel direction, can be guaranteed in connection with the modules adjacent to the bearing plate, in accordance with the solution presented in U.S. Pat. No. 7,614,227 B2.
The gerotor pumps used as oil pumps in internal combustion engines serve for engine lubrication there, which has to be guaranteed over a temperature range of minus 40° C. all the way into the range of hot idle operation of approximately 160° C., for example, in motor vehicles.
Because almost all pump housings are produced from different materials, for reasons of cost and weight savings, such as the gear wheel sets disposed in the pump housing, in each instance, for example the pump housings are often produced from die-cast aluminum and the gear wheel sets are produced from sintered steel, the axial play between the gear wheel set and the pump housing necessarily changes over the great working range/temperature range of minus 40° C. to approximately 160° C., on the basis of the different heat expansion coefficients of aluminum and steel, as a function of the current operating temperature, in each instance. In this connection, friction losses mostly occur at low operating temperatures, as a result of tight dimensions, and losses in the degree of volumetric effectiveness occur at high operating temperatures, as a result of overly great gap dimensions, which losses can amount to as much as 50% to 60% of the most advantageous degree of volumetric effectiveness for the gear ring pump arrangement, in each instance.
In this connection, the degree of volumetric effectiveness decreases in approximately linear manner with increasing temperatures.
In the state of the art, the most varied solutions for optimizing the axial gap/axial play have therefore been proposed.
For example, a gear ring pump used as an oil pump is known from DE 103 31 979 A1, the axial play of which is optimized using spacer elements disposed in the region of the screw connections between the pump lid and the pump flange, in that these spacer elements have a lower heat expansion coefficient than the pump lid, the pump flange and/or the gear wheel set.
The axial play is reduced at high temperatures and increased at low temperatures as the result of the installation of such spacer elements, which are made of nickel steel, for example.
The installation of such spacer elements leads to an increase in the degree of volumetric effectiveness as compared with conventional pumps made of die-cast aluminum having gear wheel sets made of steel, of up to 40 to 50%, but in this connection it has the disadvantage that this solution requires a significant radial enlargement of the construction space of the respective pump since the spacer elements necessarily have to be disposed outside of the pump rotor diameter and within the pump housing.
A design of a gear ring pump that can be built with a smaller outside diameter is known from DE 10 2008 054 758 A1. In this design, two housing parts that are connected with one another and surround the gerotor are braced by means of suitable spring elements, relative to one another, in addition to the connection force, in order to minimize the axial gap.
However, this solution has the disadvantage that because of the components that lie against the rotor under spring bias, friction moments necessarily occur at the face side of the rotor, which result in great losses in the degree of effectiveness.
At the same time, the production and installation effort necessarily increases as the construction size decreases, on the basis of the construction and function elements integrated into the pump housing, such as the bearing locations for the drive shaft, the suction and pressure kidneys disposed in the pump housing, and the related connection channels.
Furthermore, the gap geometries have an over-proportional negative effect on the degree of effectiveness as the construction size decreases.
In order to now reduce the production precision and thereby the production effort, particularly as the construction size decreases, it was proposed, in the state of the art, to construct these housings, particularly of small gear ring pumps, in modular manner, i.e. to join them together from multiple components.
In these embodiments, elastomer seals are disposed between the adjacent components, in order to equalize tolerances.
In these solutions having elastic tolerance equalization, “residual tensions” necessarily occur when the adjacent components are braced against one another, and these in turn lead to friction moments at the face sides of the rotor set.
If, however, the adjacent components are braced against one another “just until” tolerance-related gaps still remain between them, then leakage losses occur at the rotor set, on the face side, with an increasing operating temperature, which losses, as has already been explained, have an over-proportionally great negative influence on the degree of effectiveness of gear ring pumps that have a very small construction.
In order to now reduce these losses in degree of effectiveness that result from leakage losses or from “bracing” of the elastomer seals against the rotor set, the production precision and thereby the production effort must be over-proportionally increased for axial gap compensation, particularly in the case of gear ring pumps having a very small construction.
In the state of the art, axially displaceable sealing plates disposed adjacent to the pump rotor set on both sides are also used for axial gap compensation, where cavities enclosed by elastomer seals are disposed on the side of the plates facing away from the pump rotor set, which cavities then have pressure applied to them in the operating state of the pump.
However, in the case of gear ring pumps having a small construction, this solution with axially displaceable sealing plates disposed adjacent to the pump rotor set on both sides is specifically not suitable for achieving an optimal degree of effectiveness at justifiable production costs.
However, at the same time, the use of these axially displaceable sealing plates with pressure application to a cavity disposed between the adjacent components and enclosed by elastomer seals brings about the result that furthermore, the interior cavity pressure also acts on the edge side of the elastomer seal, so that axial tolerance equalization with elastomer seals to which pressure is applied brings about the result, with a decreasing pump construction size, that the ratio of the “elastomer sealing force” and the hydraulically generated force becomes more and more disadvantageous, and that with a decreasing construction size of the gear ring pumps (e.g. in the case of gerotor pumps having a conveying volume stream of approximately 8 L/min and outside dimensions of approximately 40 mm×40 mm×40 mm), the non-calculable “interference forces” predominate, and then have a dominant effect on the overall degree of effectiveness of the pump.